Findings from a Decade of Impaired Driving in the U.S.

While alcohol impaired driving rates among youth have declined in the United States, drug impaired driving appears to be on the rise. Research indicates illicit or prescribed drugs are associated with an increased rate of motor vehicle crashes, making current excessively high rates of drug impaired driving a significant public health concern. A recent study examining data from the Monitoring the Future project found that just over one out of every four (28%) of high school seniors were a driver or drove with someone under the influence of alcohol or other illicit drugs, with the percentage of seniors driving after smoking marijuana almost three times more than alcohol impaired drivers.

What did they do?

Since the leading causes of mortality and morbidity for youth are motor vehicle crashes, researchers Patrick M. O’Malley, PhD and Lloyd D. Johnston, PhD at the Institute for Social Research at University of Michigan studied the prevalence, trends, and correlates of driving or riding after the use of alcohol or other drugs amongst high school seniors.

The researchers analyzed 2001 through 2011 self-reported data from the Monitoring the Future project, which included a national representative sample of 17,000 high school seniors from 135 schools. From the data analysis, the researchers wanted to answer questions about high school seniors’ behavior regarding: driving after using marijuana, using other illicit drugs, drinking any alcohol, or having five or more drinks; and riding in a vehicle whose driver had used marijuana, used other illicit drugs, drunk any alcohol, or had five or more drinks. To identify which respondents are most likely to report impaired driving and riding behaviors and associated consequences (tickets, warnings for moving violations, and accidents), the researchers incorporated a variety of demographic and lifestyle indicators, such as gender, parental education, race/ethnicity, religious commitment, grade point average, and truancy.

What did they find?

Researchers determined the data confirms the increasing trend of driving after marijuana use or riding in a vehicle whose driver has used marijuana. In fact, from 2009 to 2011, the percentage of high school seniors reporting driving after marijuana use was almost three times as high as those reporting only heavy drinking prior to driving (8.6% vs. 2.9%).

Driving after drinking alcohol decreased in both categories (drank five alcohol beverages or more and drank less than five alcoholic beverages). However, the rate of change of drivers consuming five drinks or more compared to less than five drinks has been slower (8.5% vs. 7.4%). Additionally, drivers reporting marijuana use, heavy drinking, or both compared to drivers reporting neither had higher rates of receiving a ticket or warning for a moving infraction and being involved in an accident.

The finding most indicative of a serious problem for individuals and the community at large is the 28% of high school seniors (class of 2011) reporting at least one time in the past two weeks they were a driver or passenger in a car when the driver was under the influence of marijuana, alcohol, or an illicit drug. A higher percentage of passengers rode with marijuana impaired drivers than alcohol impaired drivers (20.4% vs. 15.2%).

Another interesting finding discovered by the researchers suggests the risky behaviors of impaired driving and riding with those impaired are not strongly associated with any specific demographic characteristic. This suggests driving or riding with a driver after using alcohol, marijuana, or illicit drugs is a widespread problem among various populations, each needing specific intervention plans. However, the study did identify a number of relationships between impaired driving and lifestyle factors. For instance, students with strong religions commitment and good grades were less likely to drive impaired. Additionally, students with greater amounts of truancy, evenings out per week, work hours per week, and driving miles per week were more likely to drive impaired.